1. Field of the Invention
The present invention relates to a method of controlling the baking for foods, for instance a biscuit, cookie, sponge cake, bread, snack confectionery, beans and the like.
2. Related Art
Hithereto, the baking of foods has been controlled under basic factors of baking temperature and baking period of time. Namely, an expert sets a certain standard baking temperature and baking period of time through his careful experiments, wherein states of baking on the food are checked by taking browning, water content, taste and others into consideration. Then, a worker operates the baking apparatus based on said controlling factors of the standard baking temperature and baking period of time, which may be trimmed by manual control to provide final baked products having quality same with or near to that of a standard product.
Such standard baking temperature and baking period of time, as controlling factors for baking, become guidelines with a good reproducibility to provide baked products of substantially same quality, when the products are obtained with use of same type baking apparatus. However, it has often been experienced that a quality of baked products is quite different, even if the baking temperature and baking period of time are set to same values, when the products shall be obtained with use of baking apparatus in different type.
The inventors have carefully studied and investigated in various view points, as to cause of such phenomenone to find that even if an environmental or surrounding temperature and staying period of time of the food in the baking apparatus are set in same values, a heat transfer rate of conduction heat transmitted to the food to be heated and/or intensity of heat to be radiated thereto from a heat sorce or inner wall of the baking apparatus are different, due to a difference in structure of the type of selected baking apparatus and a delicate or slight change in its operating condition, to give remarkable influence on baking degree of the food.
This will be explained in more detail, as to case, wherein a heated air forcedly circulating type home gas oven "A" or a natural convection type home gas oven "B" is employed as the baking apparatus. In the first place, the environmental temperature in these ovens "A" and "B" was set at 180.degree. C. A copper test piece painted with a thermal resistance black paint and a thermocouple is incorporated therein was put in each oven to measure temperature changes with an interval. Results are shown in FIG. 1. The test piece was painted in black to absorbe major part of the radiation heat, in addition to the conduction heat, so that it can be said that temperature rising speed of the test piece shows a total heating ability of the oven, as sum of the conduction heat and radiation heat to be generated by the oven. Judging the results shown in FIG. 1, by taking the fact into consideration, the temperature rising speed of the test piece in oven "A" is remarkably high, in comparison with that in oven "B" and thus the former oven is more excellent than the latter in its total heating ability.
The sum of conduction heat and radiation heat has generally been called as --an apparent heat transfer rate (h)--, and an amount of heat (kcal/hr) transmitted to a substance to be heated in a baking apparatus is, in general, estimated by EQU .alpha.h(T-T') (I)
wherein
h: Apparent heat transfer rate (kcal/m.sup.2.hr..degree.C.), PA1 .alpha.: Suface area of the substance to be heated (m.sup.2), PA1 T: Environmental temperature (.degree.C.), and PA1 T': Temperature of the substance to be heated (.degree.C.). PA1 Oven "A": 41 (kacl/m.sup.2.hr..degree.C.), and PA1 Oven "B": 17 PA1 Q=C+.phi.R (kcal/m.sup.2.hr), PA1 wherein .phi. is the heat radiation rate of the food material. Then, at least one of factors of temperature for heating the food in the baking apparatus and an air flow rate in the food baking apparatus is controlled, based on the measured amount of the heat absorbed by the food.
As apparent from the equation (1), an amount of heat transmitted to the substance to be heated depends on 2 factors of the environmental temperature and apparent heat transfer rate. If an apparent heat transfer rate in the ovens "A" and "B" is calculated based on each temperature rising curve on the test pieces arranged in the oven on the aforesaid experiments, following results can be obtained, which show a fact that the apparent heat transfer rate bacomes quite different, depending on difference of the type of selected ovens.
Turning now to the baking per se, a baking degree of foods depends on how much thermal energy has been absorbed by the food, rather than how long the food has been kept under what environmental temperature. In this case, the amount of heat transmitted to the food is determined by the both of the environmental temperature and heat transfer rate, as shown in said equation, which means that the baking temperature and baking period of time, as having been employed as basic controlling factors for baking have a poor correspondency with the amount of heat transmitted to the food to make the appropriate control of baking for foods difficult.